Wireless power transfer systems are a well known area of both established and developing technology. Typically, a primary side (or transmitter) generates a time-varying magnetic field from a transmitting coil or coils. This magnetic field induces an alternating current in a suitable receiving coil in a secondary side (or receiver) that can then be used to charge a battery or power a load, such as a portable device.
A basic problem that must be overcome in wireless power transfer system design is ensuring that power can be transferred over sufficient displacements (i.e. between the primary side and secondary side), while maintaining a sufficient amount of power transfer.
It is known that introducing magnetically permeable elements into either the transmitting coils or receiving coils can improve the performance of the system. Magnetically permeable elements increase the inductance of the transmitter or receiver. This means that less coil turns are required to achieve the same inductance value as a transmitter or receiver without magnetically permeable elements. Having fewer coils turns results in a decrease in losses due to resistance in the coil wire. Magnetically permeable elements can also be configured to ‘shape’ the magnetic field, which can be directed from the transmitter to the receiver. By directing the magnetic field, the coupling factor between the transmitter and receiver can be increased, thus improving the performance of the system.
For wireless power transfer systems, the magnetically permeable element may be in the form of a planar sheet underneath a layer of windings. In other applications, the magnetically permeable element may be a core, about which the windings of the transmitting coils or receiving coils are wound.
It is an object of the invention to provide a magnetically permeable core for use in transmitters or receiver, which improves the tolerable displacement between the transmitter and receiver, or to at least provide the public with a useful choice.